Clutch assemblies are used in transmissions and the like to join a rotatable drive member with a rotatably driven member. Depending on the particular design, several clutch assemblies may be used in combination to establish different drive connections throughout the transmission.
Each clutch assembly includes a series of interleaved friction plates defining a clutch area. Alternate ones of the friction plates rotate with the drive member and the remaining friction plates rotate with the driven member.
A clutch actuator is used to engage the clutch assembly. A typical actuator comprises a piston-like member arranged in a fluid chamber usually defined by the drive member. The actuator applies a linear compressive force against the friction plates in a manner selectively establishing a drive connection between the drive and driven members.
During modulated engagement of the clutch assembly, the friction plates slip relative to each other. As will be appreciated, heat input results from the slipping action between the plates. Excess heat will destroy the clutch assembly thus involving timely and costly repairs. Thus, heat input must be removed before reengagement of the clutch assembly.
To dissipate heat build up, it is known to flood the clutch area with hydraulic cooling fluid. Although the cooling fluid dissipates the heat developed by the slipping friction plates, additional problems are created when the clutch area is flooded with cooling fluid.
As mentioned, several clutch assemblies may be arranged within a transmission to develop different drive connections during operation of the transmission. Each clutch assembly requires a separate cooling fluid flow thereto to dissipate the heat build up for that particular clutch assembly. As will be appreciated, to provide a sufficient cooling fluid flow to several clutch assemblies normally requires a sufficiently large fluid pump and reservoir from which the hydraulic cooling fluid is supplied under pressure, thus adding to the size, weight, and complexity of the construction.
Flooding the clutch area with cooling fluid also creates a viscous drag condition on the clutch assembly. When the clutch assembly is disengaged, the friction plates connected to the drive member may rotate relative to the friction plates connected to the driven member. The cooling fluid in the clutch area creates a viscous drag condition between the relatively rotating friction plates. This condition causes a loss in horsepower and also produces heat in the clutch assembly.